Method of welding with aluminum metal-core weld wire

ABSTRACT

Methods for forming an aluminum weld on an aluminum work surface are disclosed. The methods include providing an aluminum metal-core wire having a sheath with an outer surface and a core composition within the sheath, applying a voltage to the aluminum metal-core wire in the vicinity of the aluminum work surface to generate an arc, and melting the wire and the work surface to form the weld. The sheath is formed with an inorganic lubricant on its outer surface and the core composition includes metal powders, metal alloy powders, or combinations thereof and less than about 5% of non-metallic components or non-metallic agents based on the weight of the wire.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 09/965,142filed Sep. 27, 2001 now U.S. Pat. No. 6,933,468, which in turn is acontinuation-in-part of U.S. application Ser. No. 09/685,106 filed Oct.10, 2000 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to new and improved aluminum welding wireand more particularly to a metal-core aluminum welding wire which yieldsa high quality weld bead when used in welding components of aluminumarticles.

Aluminum weld wire is conventionally provided as a solid wire that isgenerally produced by continuously casting round bars which are thenheated to a temperature dependent on the alloy and rolled, for example,to ⅜ inch diameter. This rod is then drawn through a series of dies sothat its diameter is reduced to the required size.

One of the problems that have been associated with weld deposits formedfrom aluminum weld wire is porosity. It is important that the weld beadsbe free of porosity. The porosity observed in aluminum welds has beenattributed to a number of sources but one of the most prominent sourcesis voids caused by the release of hydrogen bubbles from the solidifyingweld metal. These bubbles are caused by the introduction of hydrogencontaining materials into the weld bead. During the welding,hydrogen-containing materials are decomposed and the hydrogen soproduced dissolves in the molten metal. Upon solidification, the lowersolubility of the hydrogen in the solid metal results in the rejectionof hydrogen in solution and the production of small voids in the weld.It has been reported that hydrogen-containing materials may enter theweld bead from a number of sources but one of the principal sources isthe welding wires themselves.

U.S. Pat. No. 3,676,309 discloses an aluminum base alloy welding wire,which is coated with an alumina-phosphate coating having a low rate ofhydration such that essentially porosity free welds are obtained. Thealuminum welding wire may be prepared by immersing the wire in a firstaqueous alkaline solution containing an anode strip, continuouslyimmersing the wire in a second aqueous alkaline solution containing acathode strip, and passing an electric current through the electrolyteswhile the wire is immersed therein. Thereafter the wire may be rinsed incold water, immersed in a passivating and neutralizing acid bath, andagain rinsed. The second part of the process is an acid electrolytictreatment.

U.S. Pat. No. 4,913,927 discloses an aluminum weld wire having an ultraclean aluminum surface, lubricated with a dual coating of an essentiallyanhydrous lower alkanol and a colloidal solid lubricant.

Japan Patent Publication (OPI) 6-304780-A to Isuzu Motors Ltd. K.K.discloses an aluminum weld wire that is tubular and filled with a flux.According to the publication the flux contains 5-10% sodium, 40-45%potassium, 5% or less oxygen, 5% or less sulfur, 5-10% fluorines, and35-40% chlorines.

SUMMARY OF THE INVENTION

One embodiment of the present invention is aluminum metal-core wire.Metal-core weld wires are generally composite tubular metal electrodeshaving a metal sheath and a core in which the core contains a corecomposition of various powdered materials. The term “metal-core” is usedhere in as it is used in the welding wire industry to refer to a corecomposition that contains primarily metallic alloying powders with lowamounts (less than about 5%) of non-metallic agents that form slag onthe weld deposit. For example, see ANSI/ANS A5.9 Specifications for BareStainless Steel Welding Electrodes and Rods. In a more particularembodiment of the invention, the aluminum metal-core weld wire comprisesan aluminum sheath and a core composition containing less than about 5%non-metallic components based on the weight of the wire. The term“non-metallic” refers to elements that are not metals or metalloids; forexample, it refers to hydrogen, carbon, nitrogen, oxygen, phosphorous,sulfur, selenium and the halides. The aluminum metal-core weld wire ofthe invention is useful for joint and surface welding. Some of theadvantages of metal-core weld wire are better penetration into the basemetal and better arc transfer characteristics (as compared to solid weldwire). Better arc transfer characteristics include better arc stability,lower spatter and better arc initiation. While steel metal-core weldwire is well known and widely used in the welding industry, aluminumweld wire has not been available commercially as a tubular metal-corewire.

In a more particular embodiment of the invention, the core compositioncontains manganese nitride and/or barium. By incorporating barium and/ormanganese nitride in the core composition, less porous and in some casesessentially nonporous welds can be formed. Barium is believed to reduceporosity by dissolving hydrogen and thus preventing hydrogen frombubbling out of the weld upon solidification. Manganese nitride isbelieved to reduce porosity by releasing nitrogen upon welding. Thenitrogen purges the hydrogen from the molten weld metal.

In manufacturing metal core wires, the core composition is blended anddeposited onto a metal strip that is formed into a tube or sheath aboutthe core composition in a forming mill. The sheath surrounding the corecomposition is drawn through reducing dies to a specified diameter. Inorder to perform the drawing operation, it is necessary to lubricate theoutside surface of the sheath as it is pulled through the reducing dies.The lubricants that are conventionally used in forming steel tubularwire are organic and contain hydrogen. These lubricants aredisadvantageous in forming aluminum metal core wire because thelubricants remain on the surface of the wire and break down duringwelding and release hydrogen. Unlike steel, molten aluminum has a highsolubility for hydrogen. As a result, the released hydrogen readilydissolves in the molten aluminum weld deposit. When the weld depositsolidifies, the hydrogen is released and creates pores and channels inthe weld rendering the weld unsuitable for most applications. Inaccordance with one embodiment of the present invention, thismanufacturing difficulty is overcome by using an inorganic lubricant inthe reducing dies. One lubricant of choice is molybdenum disulfide.

Another embodiment of the invention is a method for manufacturingaluminum metal-core wire which comprises the steps of depositing a metalcore composition containing less than 5% nonmetallic elements (based onthe total weight of the wire) onto a strip of aluminum, forming thestrip of aluminum into a tube which contains the core composition,applying an inorganic lubricant to the surface of the tube, and drawingthe tube through a plurality of reducing dies.

Another embodiment of the invention is an aluminum tube useful informing an aluminum metal-core wire which comprises an aluminum sheathcontaining a core composition therein, wherein the outer surface of thealuminum sheath is coated with an inorganic lubricant and, moreparticularly in one embodiment of the invention, molybdenum disulfide.Another embodiment of the invention is a method for forming an aluminumtube useful in forming an aluminum metal-core wire wherein the formedsheath is cleaned in a bath of tetrachloroethylene (TCE) and baked at atemperature between about 280-500° F. typically for about 1 to 4 hrs. toremove hydrogen containing materials such as moisture and TCE from thesurface of the wire.

Still another embodiment of the invention is a method for forming analuminum weld which comprises applying a voltage to an aluminummetal-core wire in the vicinity or a work surface to generate an arcwhich melts the electrode and the work surface and forms the weld.

In addition to providing aluminum metal-core wire containing a corecomposition, an aluminum metal core wire is also provided which consistsof the hollow aluminum tube or sheath and no core composition. This wireis useful in applications where the advantages of a metal-core wire aredesired but the core composition is not required to modify the weldcomposition.

DETAILED DESCRIPTION OF THE INVENTION

The aluminum metal core wire of the present invention is formed from analuminum strip, which is formed into a tube. The aluminum strip that isused in the invention can be formed from aluminum or any of the aluminumalloys that are commercially available. The 4000 and 5000 seriesaluminum alloys (as classified by The Aluminum Association) are oftenused to form the strip. Two alloys that are particularly desirable forforming the strip are 5056 and 5052. The latter is characterized in thatit contains 2.2 to 2.8% Mg and the former is characterized in that itcontains 0.05 to 0.2% Mn, 4.5 to 5.6% Mg, and 0.02 to 0.2% Cr. Aluminumstrip is available in a number of thicknesses. Strip 0.4 inch wide and0.028 inch thick has been found to be suitable for use in one embodimentof the invention. In some embodiments of the invention it may bedesirable to use thicker strip in order to increase the stiffness of thewire. In these embodiments it may be desirable to use strip about 0.039inch thick. The aluminum strip that is used in one embodiment of theinvention ranges from about 0.250 to 0.650 in. wide and about 0.010 to0.040 in. thick.

The composition of the weld wire can be adjusted to provide the weldproperties and/or to be compatible with the work piece in a manner thatis known in the art. Many of these compositions have been assigned AWSnumbers. Two of the most widely used aluminum weld wires are ER 5356 andER 4043. These weld wires contain at least about 4% and more typicallyabout 4 to 6% magnesium or silicon. In two of the embodiments, the weldwires of the invention are composed such that they meet thespecifications for these wires.

In accordance with a more general embodiment of the invention, inaddition to aluminum, the aluminum metal core wires of the presentinvention may contain one or more of the following elements (based onpercent by weight of the wire):

TABLE 1 % Si 0-15 Cu 0-7.0 Mn 0-1.5 Mg 0-5.5 Ti 0-10 Ba 0-0.5

TABLE 2¹ ER 4043 ER5356 Si 4.5-6.0 0.25 max. Fe 0.8 max. 0.4 max. Cu 0.3max. 0.1 max. Mn 0.15 max. 0.05-0.20 Mg 0.1 4.5-5.5 Cr — 0.05-0.20 Ti0.2 max. 0.06-0.20¹A number followed by the term “max.” refers to the maximum permittedlevel of an impurity.

In addition to the metals shown in Tables 1 and 2, in accordance withindustry standards, the wire may contain limited amounts of Zn, Va, Be,Sn, Si, Fe, Zr. Generally, these metals will not exceed 0.005 to 0.45%.As industry standards change and/or new standards are adopted, thecompositions of the weld, the wire, the sheath and the core compositionare easily adjusted to accommodate them.

In a more specific embodiment of the invention the wires includemanganese nitride and/or barium. It is desirable to use barium andmanganese nitride alone or in combination in an amount sufficient toprovide a weld that is essentially non-porous. Manganese nitride can beused in an amount up to about 6% of the core composition and is usuallyused in an amount of about 1 to 6%. Barium can be used in an amount upto about 1.5% of the core and is usually used in an amount of about 0.1to 1.5%. Barium is preferably added to the core as CalSiBar in an amountup to 10% by weight of the core and usually in an amount of about 1 to10%.

The sheath composition useful in select embodiments of the invention, inaddition to aluminum may contain one or more of the following elementsin the approximate weight percent (based on the sheath), illustrated inTable 3:

TABLE 3 General Typical Si 0-16.00 0-11 Fe 0-1.10 0-0.8 Cu 0-0.71 0-0.5Mn 0-0.71 0.5 Mg 0-7.10 0-5.0 Cr 0-0.50 0-0.35 Zn 0-0.40 0-0.25 Ti0-0.40 0-0.30

In the embodiments of the invention in which a core composition is usedin the wire, the core composition can be adjusted, based on the sheathalloy composition, to provide a wire which meets the desired weldcharacteristics and more particularly meets one of the American WeldingSociety (AWS) classifications for aluminum electrodes and wires aspublished in AWS A5.10. The core composition in approximate weight % inone embodiment of the invention is illustrated in Table 4 (the “typical”formulations reflect AWS standards):

TABLE 4 Powder Core Composition (%) General Typical Al powder 0-100.0075-95.00 Si 0-4.0 0-4.0 Ca 0-2.0 0-2.0 Mn 0-6.0 0-1.60 Zr 0-2.5 0-1.00Cr 0-3.33 0-.40 Ti 0-10 0-3.00 Ba 0-1.5 0-1.5

The core composition may be prepared using K₃AlF₆, Ca—Si, Mn—N, Zr—Siand/or CalSiBar alloys. These alloys have the compositions shown inTable 4 below:

TABLE 4 Alloy Compositions (%) Alloy Ca Si Fe N S O Mn Zr C Al Ba Ca—Si31.5 62.5 5.5 0 0 0 0 0 0.50 0 0 Mn—N 0 0 0 6.00 .30 .50 Bal 0 0 0 0Zr—Si 0 50.8 10.3 0 0 0 0 38.4 0.50 0 0 Cal 17.1 57.6 8.16 0 0.39 0 0 00.50 1.06 15.5 SiBar

The core composition, when it is present, generally constitutes about 6to 25% total weight of the aluminum core wire and more typically about 7to 9%. In some of the more typical embodiments of the invention, thepowders and particles making up the core composition will have anaverage particle size of about 45 micron to 250 micron. Uniformdistribution of the core composition in the drawn aluminum wire affordsuniformity of the weld deposit.

Aluminum core wire can be manufactured using wire manufacturingequipment and conditions similar to those used in the manufacture ofconventional metal core wire. Aluminum strip is drawn through formingrolls. The rolls typically include 3 pair of rolls having a forminggroove therein which roll the strip into a “U” shaped tube. The tube isfilled with the metal powder and formed to create a wire. The closingrolls typically have the following diameter sequence: 0.160 in 0.150 in0.140 in and 0.130 in. The strip must be lubricated as it is movedthrough this forming die set but because so little of this lubricantremains on the surface of the wire after the downstream drawingoperation, this lubricant can be a conventional lubricant such as asilicone oil like Dow Corning 200. The strip is generally run throughthe forming rolls at a rate of about 40 to 200 feet per minute and moretypically at a rate of 44 fpm.

Downstream from the forming die, the strip is drawn through a series ofreducing dies, typically about 7 to 8 dies which progressively becomesmaller in diameter from an initial diameter of about 0.146 inch to afinal diameter of about 0.062 inch. In one case, these dies by diameter(inch) have the sequence: 0.146, 0.120, 0.109, 0.097, 0.082, 0.069, and0.062. As the strip is drawn through the reducing dies it is lubricatedwith a hydrogen-free lubricant. In one embodiment of the invention thelubricant is molybdenum disulfide. In another embodiment it is tungstendisulfide. The rolled strip is generally drawn through the reducing diesat a rate of about 100 to 1000 feet per minute.

The invention will be illustrated in more detail by the followingnon-limiting examples:

Examples

Aluminum metal core weld wires were prepared using a 5056 aluminum alloyto form the sheath and the following core compositions:

TABLE 5 Core Compositions Ex. No. 1 2 3 4 5 6 Al powder 78.00 87.0086.00 80.00 92.00 77.00 Ca/Si alloy 2.00 0.00 2.00 2.00 2.00 0.00 Ti10.00 2.00 2.00 10.00 3.00 10.0 Mn-N alloy 6.00 6.00 0.00 6.00 1.60 6.0Zr/Si alloy 1.00 1.00 1.00 1.00 1.00 1.00 Cr 1.00 1.00 1.00 1.00 .400.00 Silicon 0.00 1.00 0.00 0.00 0.00 0.00 KAlF 2.00 2.00 2.00 0.00 0.000.00 Mn 0.00 0.00 6.00 0.00 0.00 0.00 Ba/Si 0.00 0.00 0.00 0.00 0.006.00 Total 100.00 100.00 100.00 100.00 100.00 100.00

The best weldability with minimum porosity was obtained with Examples 5and 6. Examples 1-3 exhibited some porosity. Example 4 exhibited noporosity.

Having described the invention in detail and with reference to specificembodiments thereof, it will be apparent that numerous modifications andvariations are possible without departing from the scope of theinvention as defined by the following claims.

What is claimed is:
 1. A method for forming an aluminum weld on analuminum work surface, the method comprising: providing an aluminummetal-core wire having a sheath with an outer surface and a corecomposition within the sheath, being formed with an inorganic lubricanton its outer surface, the core composition including metal powders,metal alloy powders, or combinations thereof and including less thanabout 5% of non-metallic components or non-metallic agents based on theweight of the wire; applying a voltage to the aluminum metal-core wirein the vicinity of the aluminum work surface to generate an arc; andmelting the wire and the work surface to form the weld.
 2. The method ofclaim 1, wherein the sheath is aluminum or aluminum alloy.
 3. The methodof claim 2, wherein, in addition to aluminum, the wire contains inapproximate weight percent: Si 0-15 Cu 0-7.0 Mg 0-6.0 Mn 0-1.5 Ba 0-0.5.


4. The method of claim 2, wherein, in addition to aluminum, the wirecontains in approximate weight percent: Si 0-15 Cu 0-7.0 Mg 0-6.0 Mn0-1.5.


5. The method of claim 2, wherein, in addition to aluminum, the wirecontains in approximate weight percent: Si 0-15 Cu 0-7.0 Mg 0-6.0 Ba0-0.5.


6. The method of claim 2, wherein the weld wire contains magnesium orsilicon in an amount of at least 4% by weight of the wire.
 7. The methodof claim 6, wherein, in addition to aluminum, the wire contains inapproximate weight percent: Si 4.5-6.0 Fe 0.8 max. Cu 0.3 max. Mn 0.15max. Mg 0.1 Ti 0.2 max.


8. The method of claim 2 wherein, in addition to aluminum, the wirecontains in approximate weight percent: Si 0.25 max. Fe 0.4 max. Cu 0.1max. Mn 0.05-0.20 Mg 4.5-5.5 Cr 0.05-0.20 Ti 0.06-0.20.


9. The method of claim 2, wherein the sheath is formed from a 4000 or5000 series aluminum alloy.
 10. The method of claim 9, wherein thesheath is formed from a 5052 or 5056 aluminum alloy.
 11. The method ofclaim 2, wherein the core composition contains in approximate weightpercent: Al powder 0-100.00 Si 0-4.0 Ca 0-2.0 Mn 0-6.0 Zr 0-2.5 Cr0-3.33 Ti 0-10 Ba 0-1.5.


12. The method of claim 2, wherein the core composition contains inapproximate weight percent: Al powder 75-95.00 Si 0-4.0 Ca 0-2.0 Mn0-1.60 Zr 0-1.00 Cr 0-.40 Ti 0-3.00 Ba 0-1.5.


13. The method of claim 1, wherein the core composition contains barium.14. The method of claim 13, wherein the core composition contains up to1.5 wt % barium.
 15. The method of claim 1, wherein the core compositioncontains a powder of a barium-containing alloy.
 16. The method of claim15, wherein the barium-containing alloy is selected from the groupconsisting of BaSi or calcium-silicon-barium alloy.
 17. The method ofclaim 1, wherein the core composition contains MnN.
 18. The method ofclaim 17, wherein the core composition contains about 1 to 6% MnN. 19.The method of claim 1, wherein the non-metallic components ornon-metallic agents include elements that are not metals or metalloidsselected from the group consisting of hydrogen, carbon, nitrogen,oxygen, phosphorous, sulfur, selenium and halides.
 20. The method ofclaim 2, wherein the wire contains MnN in an amount of about 1 to 6% byweight based on the total weight of the wire or barium in an amount ofabout 0.1 to 1.5% by weight based on the total weight of the wire. 21.The method of claim 2, wherein the aluminum metal-core wire consists ofa tubular sheath of aluminum or aluminum alloy.
 22. The method of claim2, wherein the core composition consists of metal powders, metal alloypowders, or combinations thereof.
 23. A method for forming an aluminumweld on an aluminum work surface, the method comprising: providing analuminum metal-core wire having a sheath with an outer surface and acore composition within the sheath, the core composition consisting ofmetal powders, metal alloy powders, or combinations thereof andconsisting of less than about 5% of non-metallic components ornon-metallic agents based on the weight of the wire; applying a voltageto the aluminum metal-core wire in the vicinity of the aluminum worksurface to generate an arc; and melting the aluminum metal-core wire andthe aluminum work surface to form the aluminum weld.
 24. The method ofclaim 23, wherein the sheath is aluminum or aluminum alloy.
 25. Themethod of claim 23, wherein the sheath of the aluminum metal-core wireis an aluminum or aluminum alloy sheath and the core composition furthercomprises silicon metal, a silicon alloy, or combinations thereof. 26.The method of claim 25, wherein the silicon alloy is selected from thegroup consisting of calcium-silicon alloy, zirconium-silicon alloy,barium-silicon alloy, and combinations thereof.
 27. The method of claim25, wherein the core composition comprises aluminum powder present asabout 75% to about 95% by weight of the core.